Direct acting mechanical bucket (DAMB) valve actuators may be produced with no valve lash adjustment. As such, DAMB operated valves may respond quickly, however, temperature changes occurring within the engine having DAMB operated valves may cause expansion or contraction of valves resulting in changes to valve event timing. For example, a change in engine load can cause engine temperatures and pressures to increase. The increased cylinder temperature can cause exhaust valve expansion. Further, the cylinder head may also expand, and the exhaust valve expansion rate may be different from the cylinder head expansion rate because the exhaust valve and the cylinder head may be formed from different materials or because the exhaust valves are cooled differently from the cylinder head. The temperature changes in the cylinder may cause changes in valve stem length and valve diameter. As a result, valve timing changes may occur by way of a valve opening and/or closing at different times as valve temperature and cylinder head temperature change. Consequently, volumetric efficiency of the engine may change during transient engine operating conditions where valve and/or cylinder head temperatures change due to changes in engine operating conditions.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method of compensating for thermal conditions during transient engine conditions, comprising: adjusting an engine air amount parameter and a cylinder residual gas amount via an engine MAP and cylinder air amount volumetric efficiency relationship in response to a rate of change of cylinder air amount; and adjusting output of an engine actuator in response to the engine air amount parameter.
By adjusting cylinder air amount and a cylinder residual gas amount via an engine manifold absolute pressure (MAP) and cylinder air amount volumetric efficiency relationship in response to a rate of change of cylinder air amount, it may be possible to account for valve temperatures that can affect engine volumetric efficiency. The change of cylinder air amount may be indicative of a valve temperature change so that cylinder air amount and cylinder residual gas may be compensated until the engine reaches an equilibrium temperature where the MAP and cylinder air amount relationship may be used without compensation.
The present description may provide several advantages. In particular, the approach can reduce vehicle emissions by providing improved engine air-fuel control. Further, the approach may also reduce engine misfires and/or slow combustion events which also may increase engine emissions. Further still, the approach provides a simple way to compensate cylinder air amount and cylinder exhaust residuals during transient engine operating conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.